Fluorescent electric discharge lamp having the phosphor particles admixed with indium powder particles



Aug. 29, 1967 R MENELLY 3,339,190

FLUORESCENT ELECTRIC DISCHARGE LAMP HAVING THE PHOSPHOR PARTICLESADMIXED WITH INDIUM POWDER PARTICLES Filed NOV. 27, 1963 FIG, 2 RICHARDA. MENELLY INVENTOR ATTORNEY United States Patent C) 3,339,100FLUORESCENT ELECTRIC DISCHARGE LAMP HAVING TI-IE PHOSPHOR PARTICLES AD-MIXED WITH INDIUM POWDER PARTICLES Richard A. Menelly, Danvers, Mass.,assignor to Sylvania Electric Products Inc., a corporation of DelawareFiled Nov. 27, 1963, Ser. No. 326,573 2 Claims. (Cl. 313-109) Thisinvention relates to fluorescent lamps utilizing an amalgam as a sourceof mercury vapor. Such amalgams are used in lamps for operation at highambient temperatures, so that the mercury vapor pressure will not riseto a value giving a serious loss in efiiciency. The efliciency isgenerally best at about 36 0, whereas lamps may have to operate underconditions in which even the ambient temperature is well above thatvalue.

Indium is a very eflective metal to use with mercury in an amalgam forsuch purposes, and the invention is particularly useful with it. The useof an indium amalgam in fluorescent lamps is shown in my copendingUnited States patent application Ser. No. 220,714, filed Aug. 31, 1962.The relationship between the amounts of indium and mercury in the lampis explained in said application.

I have now discovered that by mixing fine indium particles with thesuspension used in coating the lamp with phosphor, a coating of phosphorand indium is obtained over the inside surface of the lamp envelope, theindium being mixed uniformly with the phosphor in the coating. Thisprovides more rapid re-absorption of mercury into the indium when thelamp is extinguished, easier starting, uniform brightness along thelength of the tube, and a shorter period of coming to full brightness. Areduction from 12 minutes to 5 minutes is obtained in the latterrespect. The easier starting is from the increased conductivity alongthe envelope wall.

In addition, the lamp of my present invention gives a 2% to 4%improvement in lumen maintenance at the usual 100-hour operation pointat which fluorescent lamps are rated.

Instead of mixing the indium with the phosphor, a coating of indium canbe applied first and then the phosphor layer over it. In either case,the indium is used in the form of a suspension, and is distributed alongthe length of the lamp and around its inner surface.

Other objects, advantages and features of the invention will be apparentfrom the following specification, taken in connection with theaccompanying drawing, in which:

FIG. 1 shows a fluorescent lamp in which an indium layer is under thefluorescent layer.

FIG. 2 is a larger view of an end of the lamp, showing the layers inmore detail; and

FIG. 3 is a lamp in which the indium is mixed with the phosphor in thefluorescent layer.

In FIG. 1 and FIG. 2, a glass tube 1, sealed at its ends, has the usualelectrodes 2 at each end, supported on leadin wires 3, 4, which aresealed through the glass envelope 1 and connected to the contact prongs5, 6 extending in the usual manner from the customary bases 7.

A coating 8 of indium is on the inner surface of the tube 1, and acoating 9 of phosphor over that.

The lamp contains a filling of inert gas such as argon at a lowpressure, for example, 2 millimeters, although various other fillingscan be used, for example, one of 85% argon and helium. A small quantityof mercury is present in the lamp. The amount of mercury should besufiicient to produce the desired vapor pressure, or vapor density, butis preferably present well in excess of that amount, and in sufiicientquantity to insure enough mercury is present throughout lamp life,despite the amount of mercury lost or cleaned up by combination withvarious parts of the lamp.

3,339,100 Patented Aug. 29, 1967 A lamp bulb 1 may be coated with thecoating 8 by applying a suspension of indium in a clear vehicle byfloating, spraying or Welling-up. After application of the coating 8 thebulb is heated in a lehr at a temperature of between 520 C. and 580 C.,preferably about 550 C., and after cooling is coated with a fluorescentsuspension of phosphor in the usual manner. It is then heated in a lehrin the same temperature a second time. In each case the heating shouldbe long enough to insure that all the binder used in coating is removedby vaporization or oxidation. If the suspensions used for the indium andfor the phosphor have diflerent binders, for example, if one hasnitrocellulose and the other ethylcellulose the two coatings may be madeconsecutively, without the intermediate step of heating in a lehr andboth can be heated together afterward.

In one suitable example of a suspension for the indium, purified indiumpowder fine enough to pass through a 325 mesh screen is added to al2-second viscosity ethylcellulose vehicle specific gravity 0.860, anddispersed by rolling. The specific gravity is checked, until a value of0.870 is attained and the proportion of indium in the suspension is 10milligrams per cc. About 13 /2 cc. of this suspension is necessary tocoat a standard ISO-watt T12 tube, that is a glass tube about 72 incheslong and 1 /2 inches in diameter. The amount of indium present in thetube is thus controlled by the coating. In finishing the manufacture ofthe lamp the amount of mercury can be put into the bulb in a controlledamount in the usual manner.

Instead of using separate indium and phosphor suspension, it isgenerally more convenient to make a single suspension containing bothmaterials.

This is the preferred embodiment, shown in FIG. 3, in which the coatings8 and 9 are replaced by a single fluorescent layer 10, which containsindium particles dispersed uniformly among the phosphor particles.

One example of a suspension suitable for applying such a coating is thefollowing:

300 grams of phosphor 4.05 grams of indium 250 cc. of 12-secondethylcellulose 3.42 grams of Armeen CD, a dispersing agent Thissuspension is adjusted to a specific gravity of 15- second viscosity byadding a suitable solvent for the ethylcellulose such as amyl acetate orxylol, and to proper specific gravity to obtain proper density ofcoating on the bulb. This coating is applied to the bulb, dried andheated in a lehr to between about 520 C. and 580 C., preferably about550 C. in the usual manner. The resulting coating will have the indiumdispersed through it uniformly throughout the length of the coating.Although particular examples of the invention have been described above,various modifications can be made without extending the scope of theinvention. For example, other means may be used to disperse the indiumbroadly over the bulb wall, for example vacuum or chemical deposition.

What I claim is:

1. A fluorescent electric discharge lamp having a coating of phosphorparticles admixed with indium powder particles on the inside surface ofits envelope, the indium particles being disposed uniformly through thecoating and therefore the length of the coating.

2. The method of coating an electric discharge lamp, which comprises:applying a suspension of indium powder and phosphor powder in a lacquer,then heating to a temperature sulficient to remove the lacquer but notsuflicient to remove the indium and phosphor.

(References on following page) I 3 .4 References Cited 3,007,071 10/1961Lompe 313178 UNITED 3,152,278 10/1964 Dzlergwa 313-109 X JAMES w.LAWRENCE,Primary Examiner.

V c Wmg et-a. 10/1958 Ishler et a1. 117 33.5 5 DAVID GALVIN Emmmer-9/1959 Jones 11733.5 R. JUDD, Assistant Examiner.

1. A FLUORESCENT ELECTRIC DISCHARGE LAMP HAVING A COATING OF PHOSPHOR PARTICLES ADMIXED WITH INDIUM POWDER PARTICLES ON THE INSIDE SURFACE OF ITS ENVELOPE, THE INDIUM PARTICLES BEING DISPOSED UNIFORMLY THROUGH THE COATING AND THEREFORE THE LENGTH OF THE COATING. 